35mm frame spacing modification?

I love shooting 6x6 medium format, and prefer square format images. I thought it might be fun to attempt to modify a 35mm SLR to take square images on 35mm film. I assume the masking of the viewfinder and film plane will be quite straightforward, but I'm unsure as to how I might be able to go about adjusting the frame spacing.
Can anyone recommend a particular 35mm SLR I should seek out which has easily adjustable frame spacing? I have a Pentax ME Super and a Canon Rebel X which I'm willing to modify, although I imagine I should get a simpler, fully mechanical camera.
Any tips on the general workings on film advance mechanisms or how to adjust them?

On a older type SLR (with transport/cocking lever) you would have to change the gearing.
On a model with integrated motorized transport you would have to cope with the counter fed with the film advance signals (from perforations or toothed spindle).

The most sensible suggestion that comes to my mind is buy a TLR and forget about modifying a 35mm camera with all its inherent limitiations of resolution. A 6x6 negative would be getting close to 360% larger than 35mm and packing a substantial amount more detail in your photos.

A few Canon SLRs have IR/LED sprocket counters linked to drive, shutter, mirror and computers. I wouldn't dream at all of tinkering with these. Back to the suggestion of a basic 6x6 to play with.

As you said modifying the viewfinder would not be a problem to you (I think of a mask or square lining), I would go that way.
(However take into account that by using a mask you might cut oof part of the rays going to the meter sensor.)

And leave it by that. The hassle involved in modifying film transport should not be outweighed by the savings in film. For enlarging modify the film gate in your enlarger, or mask the film gate in the camera.

Last edited by AgX; 03-06-2013 at 03:37 PM. Click to view previous post history.

for what i can remeber 4 * 4 cameras were "quiete common" in the '50s / '60s
i am not sure but some of them did not use 135 but 126 and similar other cartridges that are no longer available.
for the sake of it you could simply mask film and finder and waste a few of any roll. quiete useless, imho.

Keep in mind that the the cocking lever does two things, it transports the film and cocks the shutter. If you modified the film transport to stop at a shorter length of film, you would end with a half cocked shutter. So this is nothing that can be done without a change of the gears, so cannot be done by us tinkerers, I believe.